1. Field of the Invention
The present invention relates to a method of dynamically scaling displayed spectral information and the apparatus for performing such method.
2. Description of the Prior Art
In a number of applications, it is desirable to display spectral information, one such application being the visual readout of energy dispersive x-ray data. In such applications, it often occurs that information is being continuously provided to the display apparatus while the x-ray analysis is carried out. A common form of the display is a histogram-type visual read-out, in which a histogram or spectrum of the data is displayed on a cathode ray tube in one or more modes such as a television raster or a vector display, or on an x-y recorder. Additionally, the information may have been previously collected and stored on some memory media, e.g. a magnetic disc. In such situations, the displayed information reflects, in the vertical direction, the quantity of information that is stored or being stored, the parameter in the horizontal direction generally being a fixed physical unit, such as an energy, wavelength or other predetermined parameter.
If often happens that as the information is fed into the visual display apparatus, there is a dynamic situation, with the levels of the analytical data increasing at least in part, while the analysis is carried out, as a consequence of which, the vertical scale for the histogram readout usually has to be increased a number of times with the increasing levels of the analytical data.
In the prior art, such increases in the vertical scale of the readout are done statically, with the scale being changed intermittently by some predetermined factor of magnification or reduction, e.g. a doubling or a halving of the vertical scale, as explained hereinafter.
In one prior art mode of changing the vertical scale of the spectrum displayed, the approach is one of fixed vertical scaling of information, in which there is made, at the outset of or during the analysis, a selection or estimate of how many units there will be in the full vertical scale, after which the vertical scale is fixed, and the image then is scaled on the basis of the pre-selected value. It so happens that where, in fixed vertical scaling, there occur data whose upper limits exceed the predetermined fixed value, such that these data do not appear on the display, as a result of which, the information obtained might be significantly misleading or inadequate.
In another mode of displaying information, known to the art, sometimes referred to as "automatic vertical scaling", a minimum threshold value is assigned to the vertical scale and when any data peak in the spectrum, or histogram display reaches such threshold value, the vertical scale of the output display is increased, e.g. doubled, to accommodate such data peaks that exceed the pre-established threshold value. While this approach permits these higher data values to be registered, it suffers the disadvantage that the entire image is immediately shrunk to a fraction (i.e., to one-half where the vertical scale is doubled) of its previous image size in the vertical direction, such reduction, or halving, being continued in intermittent steps until the vertical values of these higher data values are reached. This type of digital-type adjustment, which is, in essence, a static adjustment of the vertical output scale, is not fully desirable because of the sudden decrease in the resolution of the displayed information, such decrease in resolution being particularly undesirable for relatively small values in the output information since these small values might no longer be accurately gauged and might even shrink to such small levels as not to be discernible. Such sudden decreases impair the readability of the display.
The present invention seeks to overcome or at least alleviate the disadvantages of the above prior art techniques and to provide further advantages as well.